"If" I had the money I would go for a locker first(rear only) then lower gears. Reason being is you can climb obstacles slower if you have both rear wheels actually turning under power. The reason we have to "charge up" obstacles is we need the wheel speed of our "4(1 front and 1 rear) wheel drive" to get up without slipping! With lower gears we would still be slipping on those same obstacles because of our "limited slip"
Now with both gears and locker the only thing that will limit you is the flexibility of IFS. But hey we know these aren't Jeeps! I'll keep my A/C and other amenities!
I feel "my" need for lower gears is more for going down hill and not having to ride the brakes at all. As low as 4Lo in 1st in a 5 speed is it isn't slow enough!